Non-consumable electrode for plasma jet torches



March 31, 1970 TETSUO 'GEJO ETAL 3,5045

NON CONSUMABLE ELECTRODEFOR'PL-ASMA JET TORCHES I Fiied Jun '16. 1966 FIG. I (b) he I (c1) FIG. 2(b) United States Patent US. Cl. 313231 7 Claims ABSTRACT OF THE DISCLOSURE A non-consumable electrode for plasma jet torches effectively operable with use of an oxidizing arc gas which electrode is made of zirconium boride in its entirety or at least in those portions which contact the arc gas. a

This invention relates to techniques for generating plasma jets, and more particularly to improvements in plasma jet torches. More specifically, the invention concerns a new and improved plasma jet torch capable of using air in an arc gas.

Various methods are known for generating plasma jets. Examples of these methods are: the method wherein arc discharge, glow discharge, or the like is caused within a body of gas; the method wherein a high-frequency electric field is applied to a gas to ionize the gas; and the method wherein a gas is ionized through the use of an agent such as light, radiation, or heat.

By the method wherein arc discharge, glow discharge, or the like is used, a plasma jet of particularly high energy can be obtained, and this plasma jet can be utilized for fabrication of articles from various materials, supplying of heat, and so forth.

Known devices for carrying out this electric discharge method and utilizing the plasma jet thus generated, however, have had certain drawbacks, principally relating to economy, as will be described in detail hereinafter.

It is an object of the present invention to overcome these drawbacks by providing a plasma jet torch capable of effectively using an oxidizing gas, particularly air, as or in the arc gas.

Another object of the invention is to provide a plasma jet torch of the above stated character which has a simple construction and can be produced at relatively low cost.

According to the present invention, briefly stated, there is provided a plasma jet torch characterized in that the electrodes in entirety or at least in the parts thereof exposed to the arc gas and heat are made of zirconium boride (ZrB whereby an oxidizing gas such as air can be used in the arc gas.

The nature, details, and utility of the invention will be more clearly apparent from the following detailed description when read in conjunction with the accompanying drawing, in which like parts are designated by like reference numerals.

In the drawing:

FIGURES 1(a) and 1(b) are simplified views in vertical section showing the electrodes and essential surrounding parts of known plasma jet torches;

FIGURES 2(a) and 2(b) are vertical sectional views respectively showing the anode and cathode of a plasma jet torch embodying the invention; and

FIGURE 3 is a vertical sectional view showing the electrodes and essential surrounding parts of a preferred embodiment of the plasma jet torch according to the invention.

In FIGURES 1(a) and 1(b) are shown specific examples of known devices for generating plasma jets by 3,504,219 Patented Mar. 31, 1970 are discharge. FIGURE 1(a) shows a plasma jet torch of the so-called transfer type, in which there are provided a cathode 1 and a nozzle 2 in which the cathode 1 is coaxially disposed, and which is provided with a circulation passage 4 for electrode cooling water, are gas being introduced through the annular space 5 between the cathode 1 and the nozzle 2. In this example, an arc discharge is created between the cathode 1 and a workpiece 6, and an arc gas is introduced into the part where the arc discharge has been created to eject the arc together with the arc gas out through the nozzle thereby to produce a plasma jet 3 in the form of a flame.

FIGURE 1(b) illustrates an example of a plasma jet torch of the so-called nontransfer type, in which the nozzle structure 2 functions additionally as an anode. An electric discharge is created between the nozzle 2 and the cathode 1, and a plasma jet 3 is produced in a manner similar to that in the example of the transfer type shown in FIGURE 1(a).

For the above mentioned are gas, a reducing gas or an inert gas such as argon, hydrogen, or nitrogen is generally used. These gases, however, are expensive and give rise to economic disadvantage particularly in cases where a large quantiity of arc gas is required as in the working of materials.

Accordingly, there has been an urgent demand in various industries for devices which generate air plasma jets in which air can be used as an inexpensive arc gas.

Heretofore, in most of the plasma jet torches employing gases such as inert gases for the arc gas, tungsten has been used for the cathode, while metals such as copper have been used for the anode. However, when an oxidizing gas such as air is used for the arc gas, the electrodes are consumed at a rapid rate because of oxidation and become unserviceable in a short time.

It is contemplated in the present invention to provide a plasma jet torch which can be effectively operated with the use of an oxidizing arc gas, particularly air. We have found that such a plasma jet torch can be provided by constructing the electrodes entirely, or at least those parts which are to be contacted by the arc gas, of zirconium boride (ZrB In order to indicate more fully the nature of the present invention, the following example of embodiment thereof is set forth, it being understood that the details of this example are presented as illustrative only, and that they are not intended to limit the scope of the invention.

To a quantity of ZrB powder of a grain size of 320 mesh and finer, approximately 5 percent of 5-percent (by weight) polyvinyl alcohol is added as a binder, and the resulting mixture is blended uniformly. Next, the resulting mixture is dried, placed in a metal die of hard refractory metal, and formed under a pressure of approximaely 5 kg./cm. into a cylinder of IO-mm. diameter and 20-mm. length. This cylinder is heated to 2,000 degrees C. at a heating rate of 1,000 degrees C. per hour in a vacuum Tammann furnace at a pressure of 10* mm. Hg and then sintered at 2,000 degrees C. for one hour.

The sintered cylinder thus obtained is machined into a cathode having a bullet head at one end and a small diameter projection at the other end as shown in FIG- URE 2(b). This machined cathode is further sintered at 2,400 degrees C. for one hour in the Tammann furnace, whereupon the cathode 11 is completed.

In a similar manner, a moulded ZrB cylinder of SS-mm. diameter and 30-min. length is made and machined into an anode 12 having a center nozzle and a support flange around its periphery as shown in FIGURE 2(a).

An example of a plasma jet torch in which these electrodes are used is shown in FIGURE 3. As shown, the cathode 11 is mounted on the end of a centrally disposed cathode support 17 made of a material such as copper, and the anode 12 functioning additionally as a nozzle is mounted, coaxially with the cathode 11, on a cylindrical anode support 18 also made of a material such as copper. An annular electrical insulator 19 is disposed concentrically inside the anode support 18 at a position to surround the cathode 11 and to join the inner end of the nozzle 12. Another annular insulator 20 is disposed between the cathode support 17 and the anode support 18 at the lower part of the cathode support 17. Are gas is introduced into the torch through an inlet 21. The anode support 18 is provided with a positive connection 22 for connection to a power source. (In contrast, in a known plasma jet torch, tungsten and copper are used for the cathode and anode, respectively, as mentioned hereinbefore.)

In an actual comparison test, a torch employing ZrB electrodes as described above was used to generate a plasma jet under the operational conditions of a current of 400 amps, voltage of 54 volts, an arc gas consisting of a mixture of argon introduced at a fiowrate of 27 contact and the inner surface of the nozzle, are covered with ZrB are also quite effective. In-certain cases as that,

for example, wherein ionized gas is charged negatively and is attracted toward the anode surface, only the anode may be made of ZrB and the cathode may be made of a material such as tungsten as in the conventional practice.

What we claim is: 1. A plasma jet torch in which an arc gas containing air is used, said torch comprising an anode functioning additionally as a jet nozzle, a cathode, said anode and cathode including parts exposed simultaneously to heat and the arc gas, said parts being made of zirconium boride, means to supply the arc gas past the cathode and through the anode, and means to apply electric power to the anode and cathode.

2. A plasma jet torch for using reactive gas comprising a non-consumable electrode including at least one portion consisting of zirconium boride.

litres/min. and air at a flowrate of 10 litres/min, and an electrode gap of 15 mm. As a result, no deformation whatsoever was observable in the electrodes.

For comparison, a conventional torch employing tungsten and copper electrodes was used to generate a plasma jet under the same operational conditions as described above, whereupon it was found that the surface of the tungsten cathode was severely oxidized and that white tungsten oxide had formed on the surface. Furthermore, the nozzle part of the copper anode. was found to be severely eroded.

As indicated above, the plasma jet torch according to the present invention has excellent oxidation resistance, and, moreover, since the operational parts thereof are made of an electrically conductive ceramic having high thermionic emissivity, the plasma jet torch of the invention produces excellent results through the use of air in the arc gas.

While the invention has been described above with respect to an example of a plasma jet torch of the aforementioned nontransfer type, it will be obvious, of course,

3. A torch according to claim 2, wherein said electrode includes parts adapted to contact the reactive gas and parts shielded from said reactive gas and wherein said electrode is of zirconium boride in only those parts which contact with the reactive gas.

4. A torch according to claim 2, wherein said electrode has an exposed surface covered with a layer of zirconium boride.

5. A torch according to claim 2, wherein said electrode is a cathode.

6. A torch according to claim 3, wherein said electrode is a cathode.

7. A torch according to claim 4, wherein said electrode is a cathode.

References Cited UNITED STATES PATENTS 1,850,689 3/1932 Redeker 313-218 X 2,157,498 5/1939 Reinecke et al. 313--231 X 3,077,108 2/1963 Gage et al 313-231 X 3,093,567 6/1963 Jablonski et al.

3,042,830 7/1962 Orbach 313231 3,198,932 8/1965 Weatherly 219 3,250,893 5/1966 Nestor 3131-231X 3,274,408 9/ 1966 Louis 313--346X 3,314,876 4/1967 Ransley 313-311 X FOREIGN PATENTS 802,905 10/ 1958 Great Britain.

JOHN W. HUCKERT, Primary Examiner A. I. JAMES, Assistant Examiner U.S. c1. X.R. g 9 14s; 313 21s, 311; 315-111 

